The present invention relates in general to improving woofer efficiency and more particularly concerns novel apparatus and techniques for providing an economical compact relatively efficient loudspeaker system with relatively good performance.
From the standpoint of achieving optimum sound reproduction, the best presently known approach is that of the BOSE 901 DIRECT/REFLECTING loudspeaker system generally of the type described in U.S. Pat. No. 3,582,553. That system uses a multiplicity of full-range drivers in combination with an electronic active equalizer having more than one hundred components. The use of multiple full-range speakers helps eliminate audible resonances and avoids the disadvantages associated with woofers, tweeters and crossovers. However, the use of so many loudspeakers and components in the equalizer is costly. The more economical approach is to use a woofer, tweeter and crossover network that directs low frequency signals to the woofer and high frequency signals to the tweeter in a vented box. A typical approach is to design for a Butterworth Response characteristic in the manner described in a paper by A. N. Thiele entitled "Loudspeakers in Vented Boxes" in the May and June 1971 issues of JOURNAL OF THE AUDIO ENGINEERING SOCIETY, pp. 382-91 and 471-83. Specific loudspeaker systems using these principles are described in papers by Raymond J. Newman entitled "A Loudspeaker System Design Utilizing a Sixth-Order Butterworth Response Characteristic" in the JOURNAL OF THE AUDIO ENGINEERING SOCIETY, July/August 1973, pp. 450-56, and D. B. Keele, Jr., entitled "A New Set of Sixth-Order Vented-Box Loudspeaker System Alignments" in the JOURNAL OF THE AUDIO ENGINEERING SOCIETY, June 1975, pp. 354-60. These papers teach establishing the closed box fundamental resonance of the woofer at a frequency corresponding to the half power point in a system consisting of the loudspeaker in its enclosure together with a complementary filter of the type described by Thiele as his alignment 15. Although this approach provides a reasonably uniform frequency response above the lower half power point, efficiency is less than would be desired.
Accordingly, it is an important object of this invention to provide a woofer-tweeter loudspeaker system with improved efficiency.
It is a further object of the invention to achieve the preceding object while providing a good low frequency response.
It is still a further object of the invention to achieve one or more of the preceding objects economically.